SAN FRANCISCO, (Reuters) – A federal judge yesterday struck down a California ban on same-sex marriages as  unconstitutional, handing a key victory to gay rights advocates  in a politically charged decision almost certain to reach the  U.S. Supreme Court. But U.S. District Court Chief Judge Vaughn Walker ordered  the voter-approved ban, known as Proposition 8, to remain in  place at least temporarily until he decides a request by  supporters of the ban to keep it intact while the case moves to  a higher court.

Although the result leaves gay men and lesbian couples  unable to marry for now, Walker said Prop 8 opponents  “demonstrated by overwhelming evidence” that it violates due  process and equal-protection rights under the U.S.  Constitution. “Proposition 8 fails to advance any rational basis in  singling out gay men and lesbians for denial of a marriage  license,” Walker wrote in the conclusion of the 136-page  opinion.

Outside the federal courthouse in San Francisco, a cheer  went up among a group of about 70 same-sex marriage supporters  carrying small U.S. flags, as a large rainbow-striped flag —  the symbol of the gay rights movement — waved overhead.

California Governor Arnold Schwarzenegger, who has said he  personally supports gay marriage but would abide by the will of  voters and the courts, said the decision “affirms the full  protections and safeguards I believe everyone deserves.”

The highly anticipated ruling marked a major turning point  in a social debate that has sharply divided the American public  and its political establishment.

Gay rights advocates and civil libertarians have cast the  legal battle as a fight for equal rights, while opponents,  including many religious conservatives, see same-sex marriage  as a threat to the traditional family.